Áreas continentales y oceánica y tectónica (clase 1) GEOMORFOLOGÍA DINÁMICA (GL54C) SEMESTRE OTOÑO 2007 LUISA PINTO L. Áreas continentales y oceánica y tectónica (clase 1)

Morfología global asociada a tectónica Objetivos: - Conocer los principales rasgos morfológicos terrestres (oceánicos y continentales) - Examinar las causas de la topografía - Examinar las causas y estilos de deformación 

TEMAS A TRATAR El geoide Curva hipsométrica Relieve debido a movimiento de placas Rasgos morfológicos continentales Rasgos morfológicos oceánicos Márgenes divergentes Márgenes transformantes Márgenes continentales

EL GEOIDE Geoide De Wikipedia, la enciclopedia libre Desviación media del geoide respecto del elipsoide de revolución. Se denomina geoide (etimológicamente, "forma que tiene la Tierra"), a la superficie física definida mediante el potencial gravitatorio. Gráficamente se puede definir como la superficie de los mares en calma, prescindiendo de las mareas, prolongada bajos los continentes. Se excluyen los fenómenos orogénicos, por lo que las montañas no se incluyen en el mismo. Geométricamente es casi una elipsoide de revolución (esfera achatada por los polos). La forma del geoide puede determinarse por medio de: Medidas gravimétricas midiendo la magnitud de la intensidad de la gravedad en numerosos puntos de la superficie terrestre. Dado que es elipsoide de revolución (esfera achatada por los polos) la aceleración de la gravedad va aumentando desde el ecuador hasta los polos. Estas mediciones de la gravedad terrestre tienen que ser corregidas para eliminar las anomalías locales debido a variaciones de la densidad. Mediciones astronómicas: Se fundan en medir la vertical del lugar y ver sus variaciones. Esta variación se relaciona con su forma. Medición de las deformaciones producidas en la órbita de los satélites causadas porque la Tierra no es homogénea. Así se ha determinado un geoide con decenas de abultamientos o depresiones respecto al elipsoide de revolución teórico. Estas irregularidades son menores de 100 metros.

CURVA HIPSOMÉTRICA

RELIEVE TERRESTRE

ANOMALÍAS SÍSMICAS VS. TOPOGRAFÍA Topography and seismicity define linear anomalies that are more or less superimposed.  They are the two most obvious consequences of lithospheric deformation. 

PLACAS TECTÓNICAS

RASGOS MORFOLÓGICOS CONTINENTALES

PRINCIPALES CINTURONES OROGÉNICOS

RASGOS MORFOLÓGICOS OCEÁNICOS

OCÉANOS ASOCIADOS A FORMAS DE RELIEVE

NATIONAL GEOGRAPHIC, 1996, P. 111.

MARGENES DIVERGENTES

MARGENES DIVERGENTES Divergent plate boundaries are also regions characterised by high topography.  The average elevation of Mid-Oceanic Ridges (MORs) is pretty much constant at about 3600 m below sea level (buoyant level of the asthenosphere).  The oceanic floor has an average elevation of about 5000 m below sea level.  Therefore, MORs are oceanic mountain belts.  Isostasy acting on a thin (or non existing) oceanic lithosphere explains the high topography of MORs. East Pacific Rise forms as the Pacific and Cocos plates separate at a "fast" rate of 120 millimeters per year. Here a map depicts a 1000 km stretch of the Rise, extending from 8-17°N. The map reveals two kinds of discontinuities: large offsets, about 100 km long, known as transform faults and smaller offsets, about 10 km long, called overlapping spreading centers (detail on the right). Colors indicate depths of from 2350 (pink) to 3500 meters (dark blue). More at: http://magic.geol.ucsb.edu/~ken/sciam.html   Computer-generated detailed topographic map of a segment of the Mid-Oceanic Ridge of the East Pacific Rise. "Warm" colors (yellow to red) indicate the ridge rising above the seafloor, and the "cool" colors (green to blue) represent lower elevations. This image (at latitude 9° north) is of a small part of the East Pacific Rise. The discontinuity in the middle of the picture is called an overlapping spreading center. (Imagery of Stacey Tighe, University of Rhode Island.)  More at http://pubs.usgs.gov/publications/text/topomap.html

Características estructurales de los márgenes divergentes MARGENES DIVERGENTES Características estructurales de los márgenes divergentes Rifting, sedimentary and oceanic basins, and the formation of continental margins result from processes that tend to thin and extend the continental crust. Normal faults in the upper brittle crust and viscous flow in the ductile lower crust result from of a stress regime in tension, where the principal stress axis sigma 1 is vertical. The combined action of normal faulting and horizontal flattenning is responsible for thinning and extension of the continental crust. As seafloor spreading occur, stretching and thinning of the continental margin stops. Thermal subsidence follows so that the sedimentary pile deposited on the margins consist of pre-, syn- and post-rift packages.

MARGENES TRANSFORMANTES Topografía y borde de fallas transformantes The sign and magnitude of the topography depends on how much contraction or extension occurs across the fault.  The picture on the left shows the sharp negative topography gradient in the vicinity of the Cos transform fault that admits a component in extension (South Atlantic ocean).  In New Zealand, the Alpine transform fault admits a component in shortening which lead to the formation of a high elevated mountain belt (positive topography). The Mid-Atlantic Ridge emerges as the South American and African plates pull apart at the "slow" rate of approximately 30 millimeters per year. The axis of the ridge is marked by a 2 km deep rift valley, which is typical of most slow-spreading ridges. The map reveals a 12 km jog of the rift valley, a second-order discontinuity, and also shows a first-order discontinuity called the Cox transform fault. Colours indicate depths from 1900 m (pink) to 4200 m (dark blue). More at: http://magic.geol.ucsb.edu/~ken/sciam.html   Computer-generated detailed topographic map of New Zealand and its surroundings, showing the extend of the Alpine transform fault.  Some of the highest peaks on the southern hemisphere result from the Alpine fault.

Los Alpes del Sur es un buen ejemplo de contacto de fallas transformantes Setting of the New Zealand micro-continent (yellow-shading) stradling the obliquely convergent Australia-Pacific plate boundary zone. Numbered arrows show rates of relative convergence in mm/year. Inverted v represents active volcanic arcs. Dark blue represents anomalously thick oceanic crust of the subducting Hikurangy Plateau. This map respresents the topography of New-Zealand and its surroundings. In green to red is the continental crust most of it being under sea level. The linear anomalie running NE-SW is the boundary between the Indo-Australian plate and the Pacific plate.

CINTURONES MONTAÑOSOS SOBRE FALLAS TRANSFORMANTES The Pyrénées is a 400 km long mountain belt along the boundary between Spain and France. In the middle Cretaceous the opening of the North Atlantic ocean induced the sinistral translation of the iberic peninsula along the North Pyrenean Transform Fault. This lithospheric scale strike-slip fault created a weak zone in the continental lithosphere, and controlled the deposition of pull-apart basins and the intrusion of mantle rocks (Lherzolite). In the Eocene (40 Ma ago) convergence occurred between France and the Iberic peninsula closing the basins and developing a symmetric mountain belt.

ZONAS DE RIFT CONTINENTAL Baikal Rhine Basin and Range Rift africano

RIFT EN EL ESTE DE ÁFRICA                                                                      Map of East Africa showing some of the historically active volcanoes(red triangles) and the Afar Triangle (shaded, center) -- a so-called triple junction (or triple point), where three plates are pulling away from one another: the Arabian Plate, and the two parts of the African Plate (the Nubian and the Somalian) splitting along the East African Rift Zone. http://pubs.usgs.gov/publications/text/East_Africa.html

BASIN AND RANGE PROVINCE Despite a relatively high topography, the crust at the centre of the Basin and Range (western US) is only 22 km thick, and interestingly this region does not correspond to a plate boundary. Therefore, regions of high topography are not restricted to areas of thick continental crust.  So, what's going on? Topography in the Basin and Range Province (black rectangle) in the North American Cordillera.  Warm colours represent regions of high topography. The block diagram below represents an E-W section through the Basin and Range province.  A thermal anomaly underneath the continental crust has progressively turned the lithospheric mantle into asthenosphere (remember the base of the lithosphere is an isotherm).  As this process proceeds, the average density of the lithosphere tends towards that of the crust.  Isostasic adjustment explains the high topography of the region.                                                                        

MÁRGENES CONTINENTALES CALIFORNIA JAPON ANDES ATLÁNTICO

Margen tipo californiano La Falla de San Andrés es otro clásico ejemplo de contacto transformante.

MARGEN CONTINENTAL TIPO ATLÁNTICO

MARGEN CONTINENTAL TIPO ANDINO

ESTRUCTURAS Y MORFOLOGIAS DE UN OROGENO DE MARGEN CONTINENTAL

RASGOS GEOMORGOLOGICOS DE LOS ANDES The Andes is the best example of a mountain belt associated with a subduction zone. This belt is composed of folded and faulted mesozoic sediment (in blue) of an intracontinental basin deposited on top of a basement. This basement is made of deformed Palaeozoic rocks on top of a proterozoic crust (pink). This belt started to develop 80 Ma ago. It presents a simple fan symmetry. The belt is intruded by long (up to 1000km) granitic batholiths, and covered by volcanic rocks. South Peru=> North Bolivia=>

MARGEN CONTINENTAL TIPO JAPONÉS

ESTRUCTURAS Y MORFOLOGIAS DE UN ARCO DE ISLAS INTRAOCEANICAS ¿Dónde hay este tipo de arcos volcánicos? Buscar en el mapa de placas

BIBLIOGRAFÍA 1) Summerfield, M.A., 1991. Global Geomorphology: Prentice-Hall, 537 pp. 2) Moores, E., Twiss, R., 1995. Principal tectonic features of the Earth. In: Tectonics, capítulo 3, p. 29-48. 3) Raymond V., Ingersoll and Busby J., 1995. Classification of Sedimentary Basins. Tectonics of Sedimentary Basins, pp 2-9. (caja del curso)

LECTURAS 1) Burbank, D., Leland, J., Fielding, E., Anderson, S., Brozovic, N., Reid, M., Duncan, C., 1996. Bedrock incision, rock uplift and threshold hillslopes in the northwestern Himalayas. Nature, vol. 379, p. 505-510. 2) Burbank, D., 2002. Rates of erosion and their implications for exhumation. Mineralogical Magazine, vol. 66, p. 25-52.